In this paper, we sought to understand the biological mechanisms of five common mental illnesses so that we could learn about the relationship between the mind and body. Previous research has predicted mental health challenges by variables such as sympathetic/parasympathetic activity in obsessive-compulsive disorder, prefrontal cortex size in borderline personality disorder, amygdala activity in depressive rumination and in generalized anxiety disorder, and cerebellar activity in eating disorders. In our correlational study, we tested the strength of these relationships by examining naturalistic daily changes in their variables longitudinally over a one-week period. We measured sympathetic/parasympathetic activity by measuring heart rate, prefrontal cortex activity by EEG, amygdala activity by increases in heart rate after watching a scary video clip, cerebellar activity by a balance task, and measured by questionnaires levels of obsessive-compulsion, rumination, anxiety, borderline personality, and eating disorder. In contradiction to our predictions, data pooled across our participants showed a significant positive correlation between heart rate and obsessive compulsive disorder symptoms and there were no significant results in support of any of our other predicted relationships. These results could be helpful to understanding the biological mechanisms of obsessive-compulsive disorder. A possible practical application of these findings shows that having increased sympathetic/parasympathetic activity indicates higher obsessive-compulsive disorder symptoms.
